Babies increase mothers’ brain sizes

Research conducted at the Yale-New Haven Hospital and published this month has found that in the six months after giving birth, parts of mothers’ brains that are linked to motivation and behavior increase in size. The study, called “The Plasticity of Human Maternal Brain: Longitudinal Changes in Brain Anatomy During the Early Postpartum Period,” and conducted by National Institute of Mental Health neuroscientist Pilyoung Kim, found there was a particular increase in the grey matter area.

Researchers said the physical increase may have important functional benefits for mothers with infants, but that the change may not be permanent.

Nineteen mothers — 10 who gave birth to boys and nine who gave birth to girls — took part in the study, which was conducted in New Haven.

Pictures of the mothers’ brains were taken during two intervals: two to four weeks after birth and then again when the infants were three to four months old, Kim said. A comparison of both pictures showed that the volume of grey matter — which is an area in the brain that plays a role in sensory and motor function ­— increased significantly over that period of time.

“It would be interesting to see what the state of the brains was like at baseline (before pregnancy) and also what happens to them months and years later,” said David Greer, associate professor and vice chairman of the Department of Neurology at the School of Medicine.

Linda Mayes, a co-author of the study and a professor at the Yale Child Study Center, said the explanation behind these results lies in the physical and hormonal changes a mother experiences in the first three to six months after child birth. Mayes added that researchers have not yet ascertained whether hormonal or environmental changes play a larger role in the increase of grey matter.

Although the brains of all mothers in the study were impacted by the stresses of having a child, and by learning how to cope with raising an infant, the changes were not uniform, according to an American Psychology Association press release about the study.

“In particular, the mothers who most enthusiastically rated their babies as special, beautiful, ideal, perfect and so on were significantly more likely to develop bigger mid-brains than the less awestruck mothers,” the press release said.

A correlation between the gender of the child and increase in brain size could possibly exist, Leckman said.

But Greer said the study does not provide enough data to say whether the gender of the child plays a significant role.

Leckman added that he doubts any gender difference examined in future studies would show a sizable effect on the size of the mother’s brain.

The number of children a woman has given birth to may also play a role.

About half of the women in the study were first-time mothers while the other half had already given birth before.

“The birth of a child (especially the first child) is for most families a time of hedonic transformation,” Leckman said, adding that this change might mean that a woman’s first child has a greater impact on grey matter volume.

But when the researchers studied structural changes in the brain, they found that both first-time and second- and third-time mothers exhibited similar transformations, Kim said.

The study was published in the October issue of the scientific journal Behavioral Neuorscience.